In some locations in Egypt the Sangoma Vega 60 FXO gateway does not detect busy tone and leave the line open after other side hang up
Access the Vega 60 web GUI admin page then ...
1. On the Quick Setup set the country to US
2. Under Tones enable tone detection parameter
3. For disconnect menu set on_time - 325ms and off_time to 350ms
Once done you have to apply , save and reboot the system